Speed changing gear device having two independent gear assemblies

ABSTRACT

A speed changing gear device for an automatic transmission, comprising a main gear assembly for providing a plurality of operating positions, and an axiliary gear assembly for providing a direct drive position and a speed changing drive position. The main gear assembly includes a single-pinion type first planetary gear unit having a first sun gear, a first planetary gear, a first ring gear and a first carrier, and a single-pinion type second planetary gear unit having a second sun gear, a second planetary gear, a second ring gear and a second carrier. The auxiliary gear assembly includes a third planetary gear unit having a third sun gear, at least one third planetary gear, a third ring gear and a third carrier. The first carrier and second ring gear are fixed to each other, or selectively connected to each other by a first clutch. The first and second sun gears, and the first sun gear and second carrier are selectively connected to each other by a second and a third clutch, respectively. The first sun gear, second sun gear and second carrier are selectively inhibited from rotating by a first brake, and the second carrier is inhibited from rotating by a second brake.

CROSS-REFERENCE TO RELATED APPLICATIONS

    ______________________________________                                        Inventor    Appln. No.                                                        ______________________________________                                        Asada       07/437,838, now U.S. Pat. No. 5,007,887                           Asada et al 07/439,607, now U.S. Pat. No. 5,098,357                           Asada       07/439,699, now U.S. Pat. No. 5,049,116                           ______________________________________                                    

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a speed changing gear devicein an automatic transmission for motor vehicles such as automobiles, andmore particularly to such a speed changing gear device which is equippedwith a main gear assembly and an auxiliary gear assembly which conductrespective speed changing actions, to provide a plurality of operatingpositions.

2. Discussion of the Prior Art

A known speed changing gear device used in an automatic transmission fora motor vehicle has a plurality of planetary gear units, each of whichincludes a sun gear, a ring gear, and a carrier rotatably supporting atleast one planetary pinion meshing with the sun and ring gears. One ofthe three elements of each planetary gear unit, that is, the sun andring gears and the carrier, serves as an input element which receives arotary motion to be transmitted by the gear unit, and another elementserves as an output element which is connected to another planetary gearunit or output member of the transmission, while the rest of the threeelements is held stationary or inhibited from rotating. Thus, theplanetary gear unit is capable of transmitting a received rotary motionfrom the input element to the output element, in one of oppositedirections, so that the output speed is reduced or increased withrespect to the input speed.

A plurality of the thus constructed planetary gear units may beassembled together to constitute the speed changing gear device, so thatthe individual planetary gear units perform respective speed changingactions, since each planetary gear unit is capable of conducting anindependent speed changing action as described above. In this type ofspeed changing gear device, one of the planetary gear units (the firstplanetary gear unit) receives a rotary motion from the input member ofthe transmission, and the speed of the rotary motion is first changedduring transmission thereof through the first planetary gear unit.Thereafter, the speed of the transmitted rotary motion is furtherchanged during transmission thereof through another planetary gear unitnext to the first planetary gear unit. Alternatively, a plurality ofplanetary gear units may be assembled together such that the appropriateelements of the planetary gear units are connected to each other so asto permit these planetary gear units to cooperate with each other toconduct a speed changing action. It is also possible that the speedchanging gear device is constituted by a combination of a gear assemblyconsisting of a plurality of planetary gear units, and another planetarygear unit which is capable of conducting an independent speed changingaction. The gear assembly indicated above is constructed such that theappropriate elements of the planetary gear units are connected to eachother so as to permit these planetary gear units to cooperate with eachother to conduct a speed changing action. Irrespective of the manner inwhich the planetary gear units are assembled, the speed changing geardevice is required to meet various requirements or conditions. Forexample, the speed changing gear device should be small-sized in view oflimited installation space in the transmission system for accommodatingthe gear device. It is also desirable that the gear device is capable ofproviding as many operating positions as possible for reduced shiftingshocks, and that the number of frictional coupling elements such asclutches and brakes which must be operated when the transmission isshifted up or down is reduced to a minimum so as to facilitate controlof the gear device for shiftings of the transmission and to minimize theamount of shifting shock.

Various speed changing gear devices have been developed to satisfy therequirements as described above. For example, laid-open Publication Nos.51-48062, 54-132058 and 60-88252 of unexamined Japanese PatentApplications disclose speed changing gear devices having three planetarygear units for providing five forward drive operating positions.

The speed changing gear device as disclosed in one of theabove-identified publications No. 51-48062 has two single-pinion typeplanetary gear units and one double-pinion type planetary gear unit.This gear device is constructed such that the appropriate elements ofthese three planetary gear units are permanently connected or fixed toeach other so as to permit the planetary gear units to cooperate witheach other to perform a desired speed changing action. While fiveforward drive positions can be established by this speed changing geardevice, the smallest speed reduction ratio available on this gear deviceis "1", that is, the gear device is not able to provide an overdriveposition whose speed reduction ratio is lower than "1". Further, whenthe transmission is shifted up or down, the speed changing gear devicerequires disconnection of one element of the gear device from the inputmember of the transmission, and connection of another element to theinput member, and at the same time requires releasing the currentlyfixed element from a stationary member and fixing another element to thestationary member, whereby a considerable amount of shifting shock isinduced. Therefore, the disclosed speed changing gear device requiresintricate regulation of the timings at which the frictional couplingelements are engaged or disengaged, for reduced shifting shocks. In thisspeed changing gear device wherein the appropriate elements of differentplanetary gear units are fixed to each other, it is practicallyimpossible to convert this gear device having five forward-drivepositions into those having four and three forward-drive positions.Thus, this gear device suffers from relatively low versatility andcannot be so widely used for various types of transmission.

On the other hand, the speed changing gear device as disclosed in theabove-identified publication No. 54-132058 has a combination of aRavigneaux type planetary gear assembly and a single-pinion typeplanetary gear unit. Some operating positions of the gear device areestablished while the gear assembly and the gear unit are operatedindependently of each other. Specifically, the speed of the input rotarymotion is first changed during transmission thereof through theRavigneaux type planetary gear assembly, and the speed of the rotarymotion transmitted from the gear assembly is further changed duringtransmission thereof through the single-pinion type planetary gear unit.In the other operating positions, the appropriate elements of the gearassembly and gear unit are connected to each other, so that the gearassembly cooperates with the gear unit to perform a desired speedchanging action. In this arrangement, it is practically impossible toeliminate the single-pinion type planetary gear unit and thereby convertthe present gear device having five forward-drive positions into thosehaving fewer forward-drive positions. Thus, the speed changing geardevice disclosed in this publication also suffers from relatively lowversatility. Further, the present device requires a total of threefrictional coupling elements to be operated for engagement ordisengagement, when the transmission is shifted up from the 3rd-speedposition to the 4th-speed position. Consequently, the shifting to thefrequently used position (4th-speed position) requires intricate controlof the three coupling elements of the gear device, so as to avoidincreased shifting shocks.

The speed changing gear device as disclosed in the above-identifiedpublication No. 60-88252 is constituted by a first, a second and a thirdsingle-pinion type planetary gear unit, for providing five forward-drivepositions including an overdrive position and one reverse position. Inthis gear device, the 2nd-speed position is established such that thethree planetary gear units conduct respective speed changing actions oneafter another during power transmission through the gear device. Whenthe gear device is placed in the other positions, however, the mutuallyconnected three planetary gear units cooperate with each other toconduct the relevant speed changing action. In this case, too, it ispractically impossible to convert the present gear device into thosehaving fewer operating positions. Further, the speed changing geardevice disclosed in this publication suffers from a relatively largegear ratio ρ of the planetary gear units, which unfavorably increasesthe radial size of the gear device.

The conventional speed changing gear devices as described above areconstructed such that the appropriate elements of the planetary gearunits are connected to each other, so that the gear units as a wholecontribute to a speed changing action for a desired operating position.Therefore, these planetary gear units cannot be radially spaced fromeach other and must be disposed in series coaxially with each other.Such a speed changing gear device can be suitably installed on thefront-engine rear-drive type of vehicle, but not on the front-enginefront-drive type of vehicle wherein the power transmission system mustbe accommodated in a casing having a relatively limited axial length.

SUMMARY OF THE INVENTION

The present invention was developed in the light of the situationsdescribed above. It is accordingly an object of the invention to providea speed changing gear device in an automatic transmission for a motorvehicle, which is simple in construction, assuring reduced shiftingshocks and easy control of the gear device for shifting operations.

The above object may be attained according to the principle of thepresent invention, which provides a speed changing gear device for anautomatic transmission having an input member and an output member,comprising a main gear assembly disposed between the input member andthe output member for providing a plurality of operating positionsincluding at least four forward-drive positions and one reverseposition, and including a single-pinion type first planetary gear unithaving a first sun gear, a first planetary pinion meshing with the firstsun gear, a first ring gear meshing with the first planetary pinion, anda first carrier rotatably supporting the first planetary pinion, and asingle-pinion type second planetary gear unit having a second sun gear,a second planetary pinion meshing with the second sun gear, a secondring gear meshing with the second planetary pinion, and a second carrierrotatably supporting the second planetary pinion, and an auxiliary gearassembly disposed between the input member and the output member forproviding a direct drive position whose speed reduction ratio is 1, anda speed changing drive position whose speed reduction ratio is otherthan 1, and including a third planetary gear unit having a third sungear, at least one third planetary pinion meshing with the third sungear, a third ring gear meshing with the above-indicated at least onethird planetary pinion, and a third carrier rotatably supporting the atleast one third planetary pinion. The main gear assembly furtherincludes (a) one of fixing means for fixing the first carrier and thesecond ring gear to each other, and first clutch means for selectivelyconnecting the first carrier and second ring gear to each other, (b)second clutch means for selectively connecting the first sun gear andthe second sun gear to each other, (c) third clutch means forselectively connecting the first sun gear and the second carrier to eachother, (d) first brake means for selectively inhibiting the second sungear and from rotating, and (e) second brake means for selectivelyinhibiting the second carrier from rotating.

Where the first carrier and the second ring gear are fixed to eachother, these two elements may be separate members secured to each otherby a suitable method. Alternatively, the two elements may be formed as asingle integral member which attains two functions corresponding to thetwo elements. In the latter case, too, the two elements are interpretedto be fixed to each other by fixing means, according to the principle ofthe present invention. The clutch means indicated above may be a clutchwhich is engaged for connecting the appropriate two elements indicatedabove.

In the speed changing gear device of the present invention constructedas described above, the main gear assembly can provide at least fourforward-drive positions by itself, and the auxiliary gear assemblycontributes to a speed changing action of the gear device only when thecurrently established operating position of the main gear assembly has aspeed reduction ratio which is higher or lower than that of apredetermined one of these at least four positions. Therefore, the speedchanging gear device as a whole is able to provide a total of at leastfive forward-drive positions. Namely, the main gear assembly is adaptedto establish the operating position having the highest speed reductionratio, when the gear assembly receives a rotary motion from the inputmember of the transmission while the sun gears of the first and secondplanetary gear units are connected to each other, and while the carrierof the second planetary gear unit is inhibited from rotating. If the sungears of the first and second planetary gear units rather than thesecond carrier are inhibited from rotating, the speed reduction ratioprovided by the main gear assembly becomes slightly lower than thehighest speed reduction ratio. Further, when two of the three elements(sun and ring gears and carrier) of each of the first and secondplanetary gear units are rotated at the same speed, the speed reductionratio is "1", that is, the main gear assembly is placed in the directdrive position. When the carrier of the second planetary gear unitreceives a rotary motion from the input member of the transmission whilethe sun gear of the second planetary gear unit is inhibited fromrotating, the speed reduction ratio provided by the main gear assemblyis lower than "1". In the case where the auxiliary gear assembly isadapted to conduct a speed reducing action while the main gear assemblyis placed in the 1st-speed and 2nd-speed positions, for example, thespeed changing gear device will be able to provide a total of fiveforward drive positions. Namely, the 1st- and 2nd-speed positions of thegear device are established when both the main and auxiliary gearassemblies contribute to the speed changing actions for these operatingpositions. The 3rd-speed position of the gear device is established whenthe main gear assembly is placed in its 2nd-speed position while theauxiliary gear assembly does not contribute to the speed changing action(i.e., the auxiliary gear assembly is in the direct drive position).Similarly, the 4th- and 5th-speed positions of the gear device areestablished when the main gear assembly is placed in its 3rd- and4th-speed positions, respectively, while the auxiliary gear assemblydoes not contribute to the speed changing actions. In the case where theauxiliary gear assembly is adapted to increase the speed of the inputrotation, such a speed increasing action of the auxiliary gear assemblyis conducted while the main gear assembly is placed in the 3rd- and4th-speed positions. In this case, too, a total of five forward drivepositions can be established by the speed changing gear device.

The instant speed changing gear device can be easily modified byeliminating the auxiliary gear assembly and connecting the input andoutput members of the transmission directly to the main gear assembly,so that the modified gear device having only the main gear assembly hasa reduced number of operating positions, for example, four forward-drivepositions and one reverse position. Thus, the speed changing gear deviceaccording to the present invention can be widely used in various typesof transmission. It is also to be noted that the main gear assembly andthe auxiliary gear assembly operate independently of each other duringpower transmission of the gear device. That is, the main gear assemblydoes not cooperate with the auxiliary gear assembly to perform its speedchanging action. Therefore, these two gear assemblies are notnecessarily disposed on the same axis, but may be disposed on differentparallel axes so as to reduce the axial length of the speed changinggear device as a whole, for improved installation adaptability to thevehicle body, particularly, to the front-engine front-drive vehicle.

The auxiliary gear assembly may be interposed between the output memberof the transmission, and the first carrier and second ring gear of themain gear assembly. In this case, the first sun and ring gears areselectively connectable to the input member of the transmission throughrespective clutch means. Alternatively, the auxiliary gear assembly maybe interposed between the input member of the transmission, and thefirst ring gear and second and third clutch means of the main gearassembly, with the third ring gear being fixed to the input member. Inthis case, the first sun and ring gears are selectively connectable tothe third carrier.

The auxiliary gear assembly is placed in the direct drive position whileone of the operating positions of the main gear assembly which iscurrently established has a speed reduction ratio which is higher orlower than that of a predetermined one of the operating positions.

The third planetary gear unit may be a single-pinion type planetary gearset having one planetary gear pinion, or may be a double-pinion typeplanetary gear set having at least one pair of planetary gear pinions.

The main gear assembly and the auxiliary gear assembly may be disposedin series coaxially with each other, or may be disposed on differentaxes which are parallel with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and optional objects, features and advantages of the presentinvention will become more apparent by reading the following detaileddescription of presently preferred embodiments of the invention, takenin connection with the accompanying drawings, in which:

FIGS. 1A, 2, 3A, 4A and 5 are schematic views showing differentembodiments of the speed changing gear device of the present invention;and

FIGS. 1B, 3B and 4B are views indicating the operating states ofindividual clutches and brakes in relation to the operating positions ofthe speed changing gear devices of FIG. 1A, 3A and 4A, respectively,FIGS. 1B and 4B also indicating the speed reduction ratios of the geardevices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1A, there is shown one embodiment of the speedchanging gear device of the present invention, which has a main gearassembly 4 including a first and a second planetary gear unit 1, 2, andan auxiliary gear assembly 5 including a third planetary gear unit 3.The main gear assembly 4 and auxiliary gear assembly 5 are disposed inseries coaxially with each other, such that the main gear assembly 4 islocated adjacent to the input member of the transmission in the form ofan input shaft 6, while the auxiliary gear assembly 5 is locatedadjacent to the output member of the transmission in the form of anoutput shaft 8.

The first planetary gear unit 1 of the main gear assembly 4 is asingle-pinion type planetary gear set whose major elements consist of afirst sun gear 1S, a first planetary pinion 1P meshing with the firstsun gear 1S, a first ring gear 1R coaxial with the first sun gear 1S andmeshing with the first planetary pinion 1P, and a first carrier 1Crotatably supporting the first planetary pinion 1P. The second planetarygear unit 2 of the main gear assembly 4 is also a single-pinion typeplanetary gear set whose major elements consist of a second sun gear 2S,a second planetary pinion 2P meshing with the second sun gear 2S, asecond ring gear 2R coaxial with the second sun gear 2S and meshing withthe second planetary pinion 2P, and a second carrier 2C rotatablysupporting the second planetary pinion 2P.

The elements of these two planetary gear units 1, 2 of the main gearassembly 4 are connected to each other in the following manner. Namely,a first clutch K1 is provided to selectively connect the input shaft 6and the ring gear 1R of the first planetary gear unit 1, while a secondclutch K2 is provided to selectively connect the input shaft 6 and thesun gear 1S of the first planetary gear unit 1. The carrier 1C of thefirst planetary gear unit 1 and the ring gear 2R of the second planetarygear unit 2 are integrally fixed to each other for rotation as a unit.Between the sun gears 1S, 2S of the first and second planetary gearunits 1, 2, a third clutch K3 is provided to selectively connect the twomembers 1S, 2S. Further, a fourth clutch K4 is provided between the sungear 1S of the first planetary gear unit 1 and the carrier 2C of thesecond planetary gear unit 2 for selective connection therebetween.

For selectively locking or holding stationary the sun gear 2S of thesecond planetary gear unit 2, there is provided a first brake B1 betweenthe second sun gear 2S and a stationary transmission casing hereinafter,referred to simply as "casing") 7. Between this casing 7 and the carrier2C of the second planetary gear unit 2, there is disposed a second brakeB2 so that the second carrier 2C is selectively held stationary or fixedto the casing 7 by the second brake B2. In the main gear assembly 4, thefirst carrier 1C and the second ring gear 2R are integrally fixedtogether to serve as an output element of the gear assembly 4, which isconnected to an input element of the auxiliary gear assembly 5 whichwill be described below.

The third planetary gear unit 3 of the auxiliary gear assembly 5 is asingle-pinion type planetary gear set whose major elements consist of athird sun gear 3S, a third planetary pinion 3P meshing with the thirdsun gear 3S, a third ring gear 3R coaxial with the third sun gear 3S andmeshing with the third planetary pinion 3P, and a third carrier 3Crotatably supporting the third planetary pinion 3P. To the third ringgear 3R is fixedly connected the output element of the main gearassembly 4, i.e., the integrally fixed first carrier 1C and second ringgear 2R. Thus, the third ring gear 3R serves as the input element of theauxiliary gear assembly 5. This third planetary gear unit 3 has twopower transmission modes, i.e., speed reduction mode wherein a rotarymotion received from the output member of the main gear assembly 4 istransmitted to an output member of the auxiliary gear assembly 5, at aspeed reduction ratio which is higher than 1, and direct drive modewhose speed reduction ratio is 1. In order to establish these two powertransmission modes, the third planetary gear unit 3 has a fifth clutchK5 disposed between the third sun gear 3S and carrier, 3C forselectively connecting these members 3S, 3C, and a third brake B3disposed between the third sun gear 3S and the casing 7 for selectivelyfixing the third sun gear 3S to the casing 7.

The output shaft 8 of the transmission is fixed to the carrier 3C of thethird planetary gear unit 3 of the auxiliary gear assembly 5.

Means for integrally fixing the elements together as indicated above maybe a suitable hollow or solid shaft or a suitable connecting drumusually employed in an ordinary automatic transmission for fixingfunctionally different elements for rotation as a unit.

The input shaft 6 is connected to an engine (not shown) of a motorvehicle through suitable power transmission means (not shown) such as atorque converter or fluid coupling. On the other hand, the output shaft8 is connected to a differential gear device (final reduction gear) ofthe power transmitting system, directly or through a propeller shaft orcounter gear.

The above-described clutches K1-K6 function to selectively connect theappropriate two elements of the speed changing gear device, i.e., areengaged for connection of the appropriate two elements when needed, andare disengaged for disconnection of the two elements from each other.For example, the clutches K1-K6 may be a wet-type multiple-disk clutch,a one-way clutch, or a combination of a wet-type multiple-disk clutchand a one-way clutch, which are operated by suitable actuators such as ahydraulic servo unit generally employed for known automatictransmissions. In the third case, the multiple-disk clutch and theone-way clutch may be disposed in series or parallel with each other. Inpractice, a suitable intermediate member such as a connecting drum isused for operatively associating the appropriate two elements of thegear device with the clutches K1-K6, since there are actually more orless restrictions in locating the clutches in the speed changing geardevice.

The first, second and third brakes B1, B2, B3 may be a wet-typemultiple-disk brake, a band brake, or a one-way clutch, or a combinationof these frictional coupling components, and may be operated by suitableactuators such as a hydraulic servo unit generally employed for knownautomatic transmissions. Certainly, there are provided suitableconnecting members as described above with respect to the clutchesK1-K6, between each brake B1, B2, B3 and the elements that are braked bythe brakes B1-B3, or between the brake and the casing 7.

The present speed changing gear device of FIG. 1A constructed asdescribed above provides a total of five forward drive positions(1st-speed, 2nd-speed, 3rd-speed, 4th-speed and 5th-speed positions),and two reverse positions (1st-speed and 2nd-speed positions). Theseoperating positions of the gear device are established by concurrentengagement of the members selected from among the five clutches K1-K5and three brakes B1, B2, B3, as indicated in the table of FIG. 1B. Inthe table, the engaged clutch or clutches and brake or brakes areindicated by "o" marks, while the disengaged clutch or clutches andbrake or brakes are indicated by blank spaces. The table also indicatesthe speed reduction ratio of each operating position of the speedchanging gear device, where gear ratios ρ₁, ρ₂, ρ₃ of the first, secondand third planetary gear units 1, 2, 3 are 0.339, 0.428 and 0.450,respectively. There will be described each of the seven operatingpositions of the instant speed changing gear device.

1ST-SPEED FORWARD-DRIVE POSITION

In the main gear assembly 4, the first clutch K1 is engaged to connectthe input shaft 6 and the first ring gear 1R, and the third clutch K3 isengaged to connect the first sun gear 1S and the second sun gear 2S,while the second brake B2 is engaged to fix the second carrier 2C to thecasing 7. Consequently, the first ring gear 1R is rotated with the inputshaft 6 while a load is applied to the first carrier 1C, whereby thefirst sun gear 1S is rotated in the reverse direction opposite to thedirection of rotation of the input shaft 6, and therefore the second sungear 2S integral with the first sun gear 1S is rotated in the samereverse direction. The term "reverse direction" will be hereinafter usedto indicate the direction opposite to the rotating direction of theinput shaft 6. In the second planetary gear unit 2, the second sun gear2S is rotated in the reverse direction with the second carrier 2C heldstationary, whereby the second ring gear 2R is rotated at a relativelylow speed, in the forward direction, i.e., in the same direction as theinput shaft 6. The term "forward direction" will be hereinafter used toindicate the direction in which the input shaft 6 is rotated. Thus, themain gear assembly 4 as a whole performs a speed reducing action so thatthe rotation of the input shaft 6 is transmitted through the firstcarrier 1C and the second ring gear 2R to the ring gear 3R of the thirdplanetary gear unit 3, whereby the third ring gear 3R is rotated in theforward direction at the speed reduction ratio of (ρ₁ +ρ₂ +ρ₁ ρ₂)/ρ₂.

In the auxiliary gear assembly 5, the third brake B3 is engaged to fixthe sun gear 3S of the third planetary gear unit 3 to the casing 7. Inthis case, the third carrier 3C is rotated at a speed lower than that ofthe third ring gear 3R, in the same direction as the third ring gear 3R.As a result, the rotary motion of the third ring gear 3R received fromthe main gear assembly 4 is transmitted to the output shaft 8 so thatthe output shaft 8 is rotated at a reduced speed as compared with thespeed of the third ring gear 3R. Thus, the third planetary gear unit 3is in the speed reduction mode as described above, in which the speedreduction ratio is represented by (1+ρ₃).

It follows from the above description that the speed changing geardevice as a whole functions to transmit the rotation of the input shaft6 to the output shaft 8 so that the output shaft 8 is rotated at aconsiderably reduced speed as compared with the speed of rotation of theinput shaft 6. The speed reduction ratio of this 1st-speed position isrepresented by (ρ₁ +ρ₂ +ρ₁ ρ₂)(1ρ₃)/ρ₂, which is equal to 3.090 asindicated in the table of FIG. 1B. In this case, no circulation of powerwill occur in the main gear assembly 4 as well as in the auxiliary gearassembly 5.

2ND-SPEED FORWARD-DRIVE POSITION

In the main gear assembly 4, the first and third clutches K1, K3, andthe first brake B1 are engaged, while in the auxiliary gear assembly 5,the third brake B3 is engaged. More specifically, the 2nd-speed positionis established by releasing the the second brake B2 and engaging thefirst brake B1 while the speed changing gear device is placed in the1st-speed position. Consequently, in the main gear assembly 4, the firstring gear 1R is rotated with the input shaft 6 while the first andsecond sun gears 1S, 2S are fixed to the casing 7 by means of the firstbrake B1. In the first planetary gear unit 1, the first ring gear 1R isrotated with the input shaft 6 with the first sun gear 1S heldstationary, whereby the first carrier 1C is rotated in the forwarddirection at a speed lower than that of the first ring gear 1R (inputshaft 6), and the rotation of the first carrier 1C is transmitted to thering gear 3R of the third planetary gear unit 3. In this 2nd-speedposition, the second planetary gear unit 2 does not contribute to aspeed changing action, since the secoind carrier 2C is not fixed to thecasing 7 and not connected to the first sun gear 1S. The speed reductionratio provided by this main gear assembly 4 represented by (1+ρ₁).

The auxiliary gear assembly 5 operates in the same manner as in the1st-speed position. Namely, the rotary motion of the third ring gear 3Rreceived from the main gear assembly 4 is transmitted to the outputshaft 8 so that the output shaft 8 is rotated at a reduced speed ascompared with the speed of the third ring gear 3R. Thus, the thirdplanetary gear unit 3 is in the speed reduction mode in which the speedreduction ratio is represented by (1+ρ₃).

It follows from the above description that the speed changing geardevice as a whole functions to transmit the rotation of the input shaft6 to the output shaft 8 so that the output shaft 8 is rotated at arelatively reduced speed as compared with that of the input shaft 6. Thespeed reduction ratio of this 2nd-speed position is represented by(1+ρ₁)(1+ρ₃), which is equal to 1.942 as indicated in the table of FIG.1B. In this case, too, no circulation of power will occur.

3RD-SPEED FORWARD-DRIVE POSITION

In the main gear assembly 4, the first and third clutches K1, K3 and thefirst brake B1 are engaged, while in the auxiliary gear assembly 5, thefifth clutch K5 is engaged. More specifically, the 3rd-speed position isestablished by releasing the third brake B3 of the auxiliary gearassembly 5 and engaging the fifth clutch K5. Namely, the main gearassembly 4 operates in the same manner as in the 2nd-speed position,i.e., performs the speed reducing action to provide the speed reductionratio of (1+ρ₁). In the auxiliary gear assembly 5, on the other hand,the fifth clutch K5 is engaged to connect the carrier 3C and sun gear 3Sof the third planetary gear unit 3, whereby the whole structure of thethird planetary gear unit 3 is rotated as a unit. That is, the auxiliarygear assembly 5 is in the direct drive mode as described above, in whichthe speed reduction ratio is "1". Thus, the rotation of the third ringgear 3R is transmitted to the third carrier 3C so that the two members3R, 3C are rotated at the same speed.

It follows from the above description that only the first planetary gearunit 1 of the main gear assembly 4 contributes to the speed reducingaction in this 3rd-speed position. Therefore, the speed reduction ratioof the speed changing gear device is represented by (1+ρ₁), which isequal to 1.339 as indicated in the table of FIG. 1B. In this case, too,no circulation of power will occur.

4TH-SPEED FORWARD-DRIVE POSITION

In the main gear assembly 4, the first and second clutches K1, K2, orthe second through fourth clutches K2, K3, K4, or the first throughfourth clutches K1, K2, K3, K4 are engaged, while in the auxiliary gearassembly 5, the fifth clutch K5 is engaged. More specifically, the4th-speed position is established by releasing the first brake B1 andengaging the second clutch K2 or the second and fourth clutches K2, K4while the speed changing gear device is placed in the 3rd-speedposition. When at least the first and second clutches K1, K2 of the maingear assembly 4 are engaged, both the first ring gear and sun gear 1R,1S are rotated with the input shaft 6, with the first planetary gearunit 1 as a whole rotating as a unit. As a result, the rotation of theinput shaft 6 is directly transmitted to the auxiliary gear assembly 5through the first planetary gear unit 1. When the second through fourthclutches K2, K3, K4 are engaged, the second sun gear and carrier 2S, 2Care rotated with the input shaft 6, with the second planetary gear unit2 as a whole rotating as a unit. As a result, the rotation of the inputshaft 6 is directly transmitted to the auxiliary gear assembly 5 throughthe second planetary gear unit 2. In other words, the main gear assembly4 placed in the 4th-speed position performs no speed changing action. Itis noted that the auxiliary gear assembly 5 also performs no speedchanging action, since the third planetary gear unit 3 is rotated as aunit with the third carrier and sun gear 3C, 3S being connected by thefifth clutch K5.

It follows from the above description that the power transmission inthis 4th-speed position occurs with the gear train of the speed changinggear device as a whole rotating as a unit. Thus, the 4th-speed positionprovides the speed reduction ratio of "1", and may be referred to as"direct drive" position, when appropriate. It will be readily understoodthat no circulation of power will occur.

5TH-SPEED FORWARD-DRIVE POSITION

In the main gear assembly 4, the second and fourth clutches K2, K4 andthe first brake B1 are engaged, while in the auxiliary gear assembly 5,the fifth clutch K5 is engaged as in the 3rd- and 4th-speed positions.More specifically, the 5th-speed position is established by releasingthe first clutch K1 and engaging the first brake B1 while the geardevice is placed in the 4th-speed position with the first, second, andfourth clutches K1, K2, K4 being engaged, for example. Consequently, inthe second planetary gear unit 2 of the main gear assembly 4, the secondcarrier 2C is rotated with the input shaft 6 with the second sun gear 2Sheld stationary, whereby the second ring gear 2R is rotated in theforward direction at a speed higher than that of the second carrier 2C.This rotary motion of the second ring gear 2R is transmitted to the ringgear 3R of the third planetary gear unit 3. In this 5th-speed position,the first planetary gear unit 1 does not contribute to a speed changingaction, since the first ring gear 1R is not connected to the input shaft6. Thus, the main gear assembly 4 provides a speed reduction ratio whichis represented by 1/(1+ρ₂). In the auxiliary gear unit 5, on the otherhand, the engagement of the fifth clutch K5 permits the third planetarygear unit 3 as a whole to be rotated as a unit. Therefore, the rotarymotion of the third ring gear 3R is directly transmitted to the outputshaft 8 as in the 3rd-and 4th-speed positions. That is, the auxiliarygear assembly 5 is in the direct drive mode as described above, in whichthe assembly 5 does not contribute to a speed changing action of thegear device.

In the 5th-speed position as described above, the speed changing of thespeed changing gear device is effected by the the second planetary gearunit 2 only, so that the speed of the output shaft 8 is increased withrespect to that of the input shaft 6. Thus, the 5th-speed position is anoverdrive position which has a speed reduction ratio lower than 1. Thespeed reduction ratio is represented by 1/(1+ρ₂), which is equal to0.700. No circulation of power will occur in this 5th-speed position.

1ST-SPEED REVERSE POSITION

The 1st-speed reverse or rear drive position is established by engagingthe second and third clutches K2, K3 and the second brake B2 of the maingear assembly 4, and the fifth clutch K5 of the auxiliary gear assembly5. In this case, too, the speed changing of the gear device is effectedby the main gear assembly 4 only, since the auxiliary gear assembly 5 isheld in the direct drive mode by the engagement of the fifth clutch K5.More specifically, the rotation of the input shaft 6 is transmitted tothe second sun gear 2S, through the second and third clutches K2, K3which are currently engaged. The concurrent rotation of the input shaft6 and the second sun gear 2S is transmitted to the second ring gear 2Rwhile the second carrier 2C is held stationary by the second brake B2,whereby the second ring gear 2R is rotated in the reverse direction at aspeed lower than that of the input shaft 6. Consequently, the reverserotation of the second ring gear 2R is transmitted to the ring gear 3Rof the third planetary gear unit 3 of the auxiliary gear assembly 5.Since the auxiliary gear assembly 5 does not contribute to a speedchanging action as in the 3rd-, 4th- and 5th-speed forward drivepositions, the speed changing of the gear device is actually effected bythe second planetary gear unit 2 only, so that the output shaft 8 isrotated in the reverse direction at a speed lower than that of the inputshaft 6. In this 1st-speed reverse position, the speed reduction ratioof the speed changing gear device is represented by -1/ρ₂, which isequal to -2.336 as indicated in the table of FIG. 1B. In this case, too,no circulation of power will occur.

2ND-SPEED REVERSE POSITION

The 2nd-speed reverse position is established by engaging the second andthird clutches K2, K3 and the second brake B2 of the main gear assembly4, and the third brake B3 of the auxiliary gear assembly 5.Consequently, the main gear assembly 4 functions to reduce the speed ofthe input shaft 6 and reverse the direction of rotation thereof, in thesame manner as in the 1st-speed reverse position. In this case, however,the auxiliary gear assembly 5 also functions to further reduce the speedof the input shaft 6. More specifically, the speed reduction ratioprovided by the main gear assembly 4 is represented by -1/ρ₂, asindicated just above, while the speed reduction ratio provided by theauxiliary gear assembly 5 is represented by (1+ρ₃), as indicated withrespect to the 1st-, 2nd-speed forward drive positions. In this2nd-speed reverse position, the speed changing of the gear device iseffected by both the main gear assembly 4 and the auxiliary gearassembly 5, so that the output shaft 8 is rotated in the reversedirection at a considerably lower speed with respect to the input shaft6. The speed reduction ratio provided by the speed changing gear deviceis represented by -(1+ρ₃)ρ₂, which is equal to -3.388 as indicated inthe table of FIG. 1B. In this case, too, no circulation of power willoccur.

It will be understood from the above explanation concerning eachoperating position of the gear device that the shiftings between the2nd- and 3rd-speed forward drive positions and between the 1st- and2nd-speed reverse positions are effected by changing the operating stateof the auxiliary gear assembly 5 while the main gear assembly 4 remainsin the same state, and that the other shiftings are effected by changingthe operating state of the main gear assembly 4 while the auxiliary gearassembly 5 remains in the same state. In the former case, the shiftingsare accomplished by releasing the currently engaged one of the thirdbrake B3 and the fifth clutch K5 of the auxiliary gear assembly 5, andengaging the other of the two members B3, K5. In the latter case, theshiftings are accomplished by releasing and engaging the appropriateones of the members selected from the clutches K1-K4 and the brakesB1-B2 of the main gear assembly 4. That is, any shifting operation ofthe present speed changing gear device does not require simultaneouscontrol of the main gear assembly 4 and the auxiliary gear assembly 5.As is apparent from the table of FIG. 1B, the speed changing gear devicehas the five forward drive positions and the two reverse or rear drivepositions, each of the seven positions being established by operatingonly two frictional coupling elements selected from the five clutchesK1-K5 and the three brakes B1-B3. Accordingly, the present gear deviceis relatively easy to control, and is free from shifting shock. Thespeed changing gear device shown in FIG. 1A is constituted by threesingle-pinion type planetary gear units which are disposed in seriescoaxially with each other. Thus, the present gear device is simple inconstruction and may be manufactured at a relatively reduced cost.Further, the gear ratios ρ of the first, second and third planetary gearunits 1, 2, 3 may be suitably determined to be around 0.34-0.45 withoutincreasing the radial size of the gear train of the gear device.Moreover, the present speed changing gear device permits the main gearassembly 4 alone to establish four forward drive positions and onereverse position. Therefore, a speed changing gear device having areduced number of operating positions can be provided by eliminating theauxiliary gear assembly 5. Furthermore, no circulation of power willoccur in any operating positions, assuring improved power transmittingefficiency. Additionally, the speed reduction rotios of the forwarddrive positions may be determined to vary in the form of a geometricalprogression, without causing a considerable change in the driving forceof the vehicle before and after the shiftings between these forwarddrive positions. Thus, the present speed changing gear drive exhibitsimproved power transmitting and speed changing characteristics. In thepresent gear device, the speeds of the three elements of each planetarygear unit 1, 2, 3, and the speeds of the planetary pinions 1P, 2P, 3Prelative to those of the carriers 1C, 2C, 3C are relatively low,assuring improved durability of the gears, bearings or other members ofthe gear device. Since the amount of load torque applied to each of thefrictional coupling elements such as clutches and brakes does not exceedthe amount of torque of the input shaft while the gear device is placedin the frequently used forward drive positions, these coupling elementsmay be made small-sized, contributing to reduction in the overall sizeof the speed changing gear device.

It will be understood from the above explanation that the main gearassembly 4 and the auxiliary gear assembly 5 are independently operatedso as to contribute to the speed changing of the speed changing geardevice. Therefore, the auxiliary gear assembly 5 is not necessarilylocated adjacent the output shaft 8, but may be located between theinput shaft 6 and the main gear assembly 4, as illustrated in FIG. 2. Inthis embodiment, the ring gear 3R of the third planetary gear unit 3 isheld fixed to the input shaft 6, while the third carrier 3C isselectively connected to the first ring gear 1R through the first clutchK1, and to the first sun gear 1S through the second clutch K2.

In this arrangement, too, the speed changing gear device can providefive forward drive positions and two reverse positions as in the firstembodiment, by operating the clutches K1-K5 and the brakes B1-B3 asindicated in the table of FIG. 1B.

The speed changing gear device of the present invention may be modifiedsuch that the auxiliary gear assembly 5 is disposed on another axisparallel to the axis on which the main gear assembly 4 is disposed, asillustrated in FIG. 3A. This arrangement is effective to minimize theamount of shifting shock of the gear device. To assure noise-freerunning of the vehicle while inhibiting an engine brake, when needed,this embodiment uses one-way clutches in combination with multiple-diskclutches and brakes.

In this modified embodiment wherein the main gear assembly 4 and theauxiliary gear assembly 5 are disposed on different parallel axes, thefirst carrier 1C and the second ring gear 2R are fixed to a counterdrive gear 9 which is located adjacent the second planetary gear unit 2,and the third ring gear 3R is fixed to a counter driven gear 10 which islocated adjacent the third planetary gear unit 3 and which engages thecounter drive gear 9. Between the second sun gear 2S and the first sungear 1S, there is provided a first one-way clutch Fl which is engaged topermit power (torque) transmission only when the second sun gear 2S andthe first sun gear 1S are rotated relative to each other in the forwarddirection. In the main gear assembly 4, the first brake B1 isconstituted by a combination of a second one-way clutch F2 and a firstmulti-disk brake 11 which are disposed in series, and a secondmulti-disk brake 12 which is disposed parallel to the combination of thetwo members F2, 11. The second one-way clutch F2 is engaged to permittorque transmission only when the second sun gear 2S is rotated in thereverse direction (in the direction opposite to the rotating directionof the input shaft 6). On the other hand, the second brake B2 isconstituted by a third one-way clutch F3 and a third multiple-disk brake13 which are disposed parallel to each other. The third one-way clutchF3 is engaged to transmit torque transmission when the carrier 2C of thesecond planetary gear unit 2 is rotated in the reverse direction. In theauxiliary gear assembly 5, the third brake B3 is constituted by a fourthone-way clutch F4 and a fourth multi-disk brake 14 which are disposedparallel to each other. The fourth one-way clutch F4 is engaged topermit torque transmission when the sun gear 3S of the third planetarygear unit 3 is rotated in the reverse direction.

The speed changing gear device shown in FIG. 3A is adapted to providefive forward drive positions and two reverse positions, as indicated inFIG. 3B, which also indicates the operating states of the clutches andbrakes, by way of example. The speed reduction ratios of the operatingpositions provided in this embodiment are substantially equal to thoseas indicated in the table of FIG. 1B.

Referring next to FIG. 4A, there is illustrated another embodiment ofthe present invention, wherein the auxiliary gear assembly 5 isconstituted by a double-pinion type planetary gear unit 13. Morespecifically, the planetary gear unit 13 includes as major elements asun gear 13S, a pair of mutually meshing planetary pinions 13P one ofwhich meshes with the sun gear 13S, a ring gear 13R coaxial with the sungear 13S and meshing with the other of the planetary pinions 13P, and acarrier 13C disposed between the sun and ring gears 13S, 13R forrotatably supporting the planetary pinions 13P. The fifth clutch isprovided between the carrier 13C and the sun gear 13S, and the thirdbrake B3 is provided between the sun gear 13S and the casing 7, as inthe preceding embodiments. However, the present embodiment is differentfrom the preceding embodiments in that the first carrier 1C and thesecond ring gear 2R of the main gear assembly 4 are fixed to the carrier13C, while the ring gear 13R is fixed to the output shaft 8. Like thefirst embodiment shown in FIG. 1, the instant speed changing gear deviceshown in FIG. 4A is capable of providing five forward drive positionsand two reverse positions, by operating appropriate ones of the couplingelements selected from the clutches K1-K5 and the brakes B1-B3, asindicated in the table of FIG. 4B. The table also indicates the speedreduction ratio of each operating position of the speed changing geardevice, where gear ratios ρ₁, ρ₂, ρ₄ of the three planetary gear units1, 2, 13 are 0.339, 0.428 and 0.311, respectively. As is apparent fromthe tables of FIGS. 1B and 4B, the speed reduction ratios obtained bythe gear device of FIG. 4A are substantially equal to those obtained bythe gear device of FIG. 1A.

While the present invention has been described in its presentlypreferred embodiments, it is to be understood that the invention is notlimited to the details of the illustrated embodiments, but may beotherwise embodied. It will be understood from the tables of FIGS. 1Band 3B that the first planetary gear unit 1 of the main gear assembly 3does not contribute to a speed changing action while the gear device isplaced in the 5th-speed forward drive position or either one of the tworeverse positions, and that the second planetary gear unit 2 does notcontribute to a speed changing action while the gear device is placed inthe 2nd-speed or 3rd-speed position. While the carrier 1C of the firstplanetary gear unit 1 and the ring gear 2R of the second planetary gearunit 2 are fixed to each other in the illustrated embodiments, there maybe provided suitable clutch means, such as a clutch K6 as shown in FIG.5, between the first carrier 1C and the second ring gear 2R, so thatthese two members 1C, 2R can be disconnected from each other so as toprevent one of the members 1C, 2R from being unnecessarily rotated withthe other member 1C, 2R when the gear device is in the 2nd-speed or3rd-speed position, that is, when the first or second planetary gearunit 1, 2 having the above one member 1C, 2R does not contribute to therelevant speed changing action. The construction of the clutch means andbrake means of the invention is not limited to those of the illustratedembodiments, but may be suitably modified. For example, the clutch orbrake means as disclosed in Japanese Patent Applications Nos. 63-176270and 63-221670 may be employed.

What is claimed is:
 1. A speed changing gear device for an automatictransmission having an input member and an output member, comprising:amain gear assembly disposed between said input member and said outputmember for providing a plurality of operating position including atleast four forward-drive positions and one reverse position, andincluding a single-pinion type first planetary gear unit having a firstsun gear, a first planetary pinion meshing with the first sun gear, afirst ring gear meshing with the first planetary pinion, and a firstcarrier rotatably supporting the first planetary pinion, and asingle-pinion type second planetary gear unit having a second gear, asecond planetary pinion meshing with the second sun gear, a second ringgear meshing with the second planetary pinion, and a second carrierrotatably supporting the second planetary pinion; an auxiliary gearassembly interposed between said input member of the transmission andsaid main gear assembly, for providing a direct drive position whosespeed reduction ratio is 1, and a speed changing drive position whosespeed reduction ratio is other than 1, said auxiliary gear assemblyincluding a third planetary gear unit having a third sun gear, at leastone third planetary pinion meshing with said third sun gear, a thirdring gear meshing with said at least one third planetary pinion, and agear meshing with said at least one third planetary pinion, and a thirdcarrier rotatably supporting said at least one third planetary pinion;said main gear assembly further including(a) one of (i) fixing means forfixing said first carrier and said second ring gear to each other, and(ii) first clutch means for selectively connecting the first carrier andsecond ring gear to each other, (b) second clutch means for selectivelyconnecting said first sun gear and said second sun gear to each other,(c) third clutch means for selectively connecting said first sun gearand said second carrier to each other, (d) first brake means forselectively inhibiting said second sun gear from rotating, and (a)second brake means for selectively inhibiting said second carrier fromrotating, and said auxiliary gear assembly being interposed between saidinput member, and said first ring gear and said second and third clutchmeans, said third ring gear being fixed to said input member.
 2. A speedchanging gear device according to claim 1, wherein said first ring gearis connected to said third carrier, and said first sun gear is connectedto the third carrier.
 3. A speed changing gear device for an automatictransmission having an input member and an output member, said speedchanging device comprising:a main gear assembly between said inputmember and said output member, for providing a plurality of operatingpositions, including at least four forward-drive positions and onereverse position, said gear assembly including a single-pinion typefirst planetary gear unit having a first sun gear, a first planetarypinion meshing with the first sun gear, a first ring gear meshing withthe first planetary pinion, and a first carrier rotatably supporting thefirst planetary pinion, and a single-pinion type second planetary gearunit having a second sun gear, a second planetary pinion meshing withthe second sun gear, a second ring gear meshing with the secondplanetary pinion, and a second carrier rotatably supporting the secondplanetary pinion; and an auxiliary gear assembly between said inputmember and said output member, for providing a direct drive positionhaving a speed reduction ratio of 1, and a speed changing drive positionhaving a speed reduction ratio of other than 1, said auxiliary gearassembly including a third planetary gear unit having a third sun gear,at least one third planetary pinion meshing with said third sun gear, athird ring gear meshing with said at least one third planetary pinion,and a third carrier rotatably supporting said at least one thirdplanetary pinion; said main gear assembly further including:(a) one of(i) fixing means for fixing said first carrier and said second ring gearto each other, and (ii) first clutch means for connecting said firstcarrier and second ring gear; (b) second clutch means for connectingsaid first sun gear and said second sun gear; (c) third clutch means forconnecting said first sun gear and said second carrier; (d) first brakemeans for inhibiting said second sun gear; and (e) second brake meansfor inhibiting said second carrier from rotating; said first planetaryunit being positioned on a side of the main gear assembly closest to theinput member, and said second planetary gear unit being positioned on aside of the main gear assembly closest to the output member, and saidfirst and second planetary gear units being placed in an axial directionof said main gear assembly; said auxiliary gear assembly beinginterposed between said input member and said first ring gear and saidsecond and third clutch means, said third ring gear being fixed to theinput member.